1. Field of the Invention
The present invention relates to a display device including the input device, and more particularly, to a display device which includes an input device of a capacity coupling type and which is suitable for achieving high coordinate detection accuracy.
2. Description of the Related Art
A display device including an input device (hereinafter, also referred to as “touch sensor” or “touch panel”) having an on-screen input function for inputting information to a display screen by a touch operation (contact and press operation, hereinafter, simply referred to as “touch”) with a user's finger or the like is used for a mobile electronic device such as a PDA or a mobile terminal, various home electric appliances, a stationary customer guiding terminal such as an automatic reception machine, and the like. It is know as the input device using the touch that there are a resistive film method of detecting a change in resistance value of a touched part, an electrostatic capacity coupling method of detecting a change in capacitance thereof, an optical sensor method of detecting a change in quantity of light at the part shielded by the touch, and the like.
The electrostatic capacity coupling method has the following advantages, compared with the resistive film method or the optical sensor method. For example, the electrostatic capacity coupling method is advantageous in that, the transmittance of the resistive film method or the optical sensor method is low about 80%, however a transmittance of the electrostatic capacity coupling method is as high as about 90%, that mean it prevents a reduction in displayed image quality. In the resistive film method, a touch position is detected by mechanical contact of the resistive film, leading to possible deterioration or breakage of the resistive film. However, in the electrostatic capacity coupling method, there is no mechanical contact such as contact of a detection electrode with another electrode. Thus, the electrostatic capacity coupling method is more advantageous in durability.
An exemplary touch panel using electrostatic capacity coupling method is disclosed in JP 2003-511799 A. In the method disclosed therein, a vertical detection electrode (X electrode) and a horizontal detection electrode (Y electrode) are arranged in vertical and horizontal two-dimensional matrix, and a capacity of each electrode is detected by an input processing unit. When a conductor such as a finger touches a surface of the touch panel, the capacity of each electrode increases. Thus, the input processing unit detects this capacity increase to calculate the input coordinates based on a signal of a capacity change detected by each electrode. Even when the detection electrode is deteriorated and the resistance value as physical characteristics is changed, its influence on capacity detection is limited. Thus, there is only a little influence on input position detection accuracy of the touch panel. As a result, high input position detection accuracy can be realized.